1. Field of the Invention
The invention relates to a combustion installation in accordance with the preamble of claim 1. It also relates to a method of operating such a combustion installation.
2. Discussion of Background
In combustion installations of standard design, the fuel is injected into a combustion chamber via a nozzle and burned there in conjunction with the feeding of combustion air. Basically, such combustion installations can be operated with a gaseous or liquid fuel. In the case of the use of a liquid fuel, the weak point as regards a clean burn in relation to the emissions of NO.sub.x, CO and UHC is evidently the necessary comprehensive atomization (gasification) of the fuel, the degree of mixing of the latter with the combustion air, and combustion at temperatures as low as possible.
A typical feature of the use of a gaseous fuel is combustion with a substantial reduction as regards pollutant emissions because, by contrast with liquid fuel, gasification of the fuel is already provided. However, gas-operated burners have not prevailed, especially in the case of combustion installations for heating boilers, despite the many advantages which such burners can offer in this connection. The reason may be that the procurement or the distribution infrastructure of gaseous fuels is an expensive matter. If, as already set out above, a liquid fuel is used, the quality of the combustion as regards lower pollutant emissions is significantly dependent upon whether success is achieved in providing an optimum degree of mixing of the fuel/fresh air mixture, i.e. in guaranteeing a complete gasification of the liquid fuel. The approach of providing a premixing zone for the fuel/fresh air mixture upstream of the actual burner does not lead to the goal of an operationally reliable burner, because there is the imminent danger here that a flashback from the combustion zone into the premixing zone could damage the burner elements.
Premixing burners have become known which are operated with 100% excess of air, so that the flame is operated shortly before the point of extinction. However, because of the boiler efficiency, an excess of air of 15% at most is permissible with combustion installations. Consequently, to operate such burners in atmospheric combustion installations with the permitted excess of air does not result in optimum operation.
Even if the degree of gasification of the liquid fuel were to be largely achieved, there would still be no effect on the high flame temperatures, which are known to be responsible for the formation of NO.sub.x. It is therefore not possible for the target combustion at low temperatures or the homogeneous mixing of the oil vapor with air to be guaranteed with the known premixing burners.